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I am learning embedded development on the STM3220G-EVAL board with the STM32F207 microcontroller. I am testing the I2C interface by interfacing the two I2C2 and I2C3 modules on the same chip and sending/receiving a character. Here is the code I have currently written:

#include <stm32f2xx.h>

volatile uint8_t data = 'a', recv = 'x';

void i2c_init(void);

// Master handler
void I2C2_EV_IRQHandler(void)
{
    volatile uint16_t stat, dummy;
    stat = I2C2->SR1;
    switch(stat)
    {
        // SB set; read SR1 and write slave address in DR to clear
        case 0x01:
            dummy = I2C2->SR1;
            // Send address of slave
            I2C2->DR = 0x40;
            break;
        // ADDR set; read SR1 and SR2 to clear
        case 0x02:
            dummy = I2C2->SR1;
            dummy = I2C2->SR2;
            break;
        // TxE set; write to DR to clear
        case 0x80:
            I2C2->DR = data;
            break;
        // TxE and BTF set; generate stop condition to clear
        case 0x84:
            // Generate stop
            I2C2->CR1 |= (1 << 9);
            break;
    }
}

// Slave handler
void I2C3_EV_IRQHandler(void)
{
    volatile uint16_t stat, dummy;
    stat = I2C3->SR1;
    switch(stat)
    {
        // ADDR set; read SR1 and SR2 to clear
        case 0x02:
            dummy = I2C3->SR1;
            dummy = I2C3->SR2;
            break;
        // STOPF set; read SR1 and write CR1 to clear
        case 0x10:
            dummy = I2C3->SR1;
            I2C3->CR1 &= ~(1 << 0);
            break;
        // RxNE set; read DR to clear
        case 0x40:
            recv = I2C3->DR;
            break;
    }
}

int main()
{
    i2c_init();
    // Generate START condition
    I2C2->CR1 |= (1 << 8);
    while(1)
    {
        if(!(I2C2->OAR1 & (1 << 14)))
            I2C2->OAR1 |= (1 << 14);
        if(!(I2C3->OAR1 & (1 << 14)))
            I2C3->OAR1 |= (1 << 14);
        if(recv != 'x')
            break;
    }
    return 0;
}

void i2c_init(void)
{
    // Enable GPIOA, GPIOC, GPIOF, I2C2 and I2C3 peripherals
    RCC->AHB1ENR |= (1 << 0);
    RCC->AHB1ENR |= (1 << 2);
    RCC->AHB1ENR |= (1 << 5);
    RCC->APB1ENR |= (1 << 22);
    RCC->APB1ENR |= (1 << 23);
    // Set GPIO mode to AF
    GPIOA->MODER |= (1 << 17);
    GPIOC->MODER |= (1 << 19);
    GPIOF->MODER |= (1 << 1);
    GPIOF->MODER |= (1 << 3);
    // Set GPIO type to OD
    GPIOA->OTYPER |= (1 << 8);
    GPIOC->OTYPER |= (1 << 9);
    GPIOF->OTYPER |= (1 << 0);
    GPIOF->OTYPER |= (1 << 1);
    // Set GPIO speed to 50MHz
    GPIOA->OSPEEDR |= (1 << 17);
    GPIOC->OSPEEDR |= (1 << 19);
    GPIOF->OSPEEDR |= (1 << 1);
    GPIOF->OSPEEDR |= (1 << 3);
    // Link to I2C AF
    GPIOA->AFR[1] |= (1 << 2);
    GPIOC->AFR[1] |= (1 << 6);
    GPIOF->AFR[0] |= (1 << 2);
    GPIOF->AFR[0] |= (1 << 6);
    // Enable interrupts
    I2C2->CR2 |= (1 << 9);
    I2C2->CR2 |= (1 << 10);
    I2C3->CR2 |= (1 << 9);
    I2C3->CR2 |= (1 << 10);
    NVIC_EnableIRQ(I2C2_EV_IRQn);
    NVIC_EnableIRQ(I2C3_EV_IRQn);
    // Must set bit 14 in OAR1 to 1
    I2C2->OAR1 |= (1 << 14);
    I2C3->OAR1 |= (1 << 14);
    // Set addresses
    I2C2->OAR1 = 0x40;
    I2C3->OAR1 = 0x40;
    // Set peripheral clock frequency
    I2C2->CR2 |= 0x08;
    I2C3->CR2 |= 0x08;
    I2C2->CCR |= 0x28;
    I2C3->CCR |= 0x28;
    I2C2->TRISE = 0x09;
    I2C3->TRISE = 0x09;
    // Enable ACK
    I2C2->CR1 |= (1 << 10);
    I2C3->CR1 |= (1 << 10);
    // Enable I2C peripherals
    I2C2->CR1 |= (1 << 0);
    I2C3->CR1 |= (1 << 0);
}

I am using a pullup of 13K on SDA and 10K on SCL. Pin numbers used are PF0, PF1 (I2C2 SDA, SCL) and PA8, PC9 (I2C3 SCL, SDA). I have not enabled I2C2 and I2C3 in RTE_Device.h. It just seems to provide convenience typedefs. (EDIT : Tried to enable these, it does not help)

The master event handler is successfully being called. But still some problems persist. The acknowledge failure bit is being set, and the slave handler is not called. Bus lines have been verified to be HIGH when idle.

Could anyone help me in solving this problem? I seem to have hit a dead end.

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  • \$\begingroup\$ Do you have an oscilloscope? Start by taking a look at the SCL and SDA lines. At least attempt to narrow the problem down to either the sending end of the receiving end. \$\endgroup\$ – Zuofu Feb 7 '14 at 16:27
  • \$\begingroup\$ Yes I have checked it with an oscilloscope, and the ACK is not being set (SDA is HIGH on 9th clock pulse). Also I noticed that the TRA bit in the I2C2 master is not set. \$\endgroup\$ – hl2gordon Feb 8 '14 at 14:40
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Sorry for the delay in mentioning this, but I have successfully solved this problem by using the STM32 CPAL library available from ST. I have tested this library with the onboard accelerometer by reading the 'WHO_AM_I' register in the accelerometer. The code for this is:

#include "cpal_i2c.h"

int main()
{
    // Configuration
    CPAL_TransferTypeDef RxStruct;
    uint8_t RxBuf;
    RxStruct.pbBuffer = &RxBuf;
    RxStruct.wAddr1 = 0x39;
    // Initialization
    CPAL_I2C_StructInit(&I2C1_DevStructure);
    I2C1_DevStructure.CPAL_Mode = CPAL_MODE_MASTER;
    I2C1_DevStructure.CPAL_ProgModel = CPAL_PROGMODEL_DMA;
    I2C1_DevStructure.pCPAL_I2C_Struct->I2C_ClockSpeed = 100000;
    I2C1_DevStructure.pCPAL_TransferRx = &RxStruct;
    I2C1_DevStructure.pCPAL_TransferTx = pNULL;
    CPAL_I2C_Init(&I2C1_DevStructure);
    // Communication
    RxStruct.wNumData = 1;
    RxStruct.wAddr2 = 0x0F;
    if(CPAL_I2C_Read(&I2C1_DevStructure) != CPAL_PASS)
    {
        // Error
    }
    while(I2C1_DevStructure.CPAL_State != CPAL_STATE_READY);
    while(1);
    return 0;
}
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  • \$\begingroup\$ Another helpful link I encountered which significantly helped me to port my code back from the CPAL library to the standard peripheral library is this: STM32F4 I2C Master tutorial \$\endgroup\$ – hl2gordon Apr 23 '14 at 19:02

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